A polycarbonate resin has been used in a wide variety of applications because the resin has excellent characteristics such as transparency, a high impact characteristic, and flame retardancy. However, when the resin is used in an application where the resin is exposed to UV light such as the outdoors, a problem in which the resin turns yellow due to the UV light occurs. Various technologies each involving blending the resin with a UV absorber to suppress the yellowing have been developed.
Meanwhile, in recent years, a polycarbonate-polydimethylsiloxane copolymer (sometimes referred to as “PC-PDMS copolymer”) has been given as an example of a polycarbonate resin material suitable for requirements for a high degree of low-temperature impact characteristic, excellent flame retardancy, and transparency. However, it is difficult to meet sophisticated requirements in the market with the PC-PDMS copolymer alone, and hence it has started to become necessary to blend the copolymer with various additives to impart sophisticated functions to the copolymer.
The impartment of the sophisticated functions to the PC-PDMS copolymer through the blending of the copolymer with the various additives has caused problems because the following trouble occurs. A phenomenon in which the PC-PDMS copolymer becomes clouded occurs at the time of the impartment to impair excellent transparency or weatherability of the copolymer.
It has been known from Patent Literature 1 and Patent Literature 2 that when a homopolycarbonate resin using bisphenol A as a monomer component is used as an optical disk substrate, an optical information recording medium having a low bit error ratio can be obtained by setting the amount of sodium remaining in the polycarbonate resin to 1 ppm or less. However, an influence of sodium remaining in a resin composition obtained by adding the various additives to the PC-PDMS copolymer has not been known.
As a result of their extensive investigations, the inventors of the present invention have found that when sodium contents in the various additives are large, a phenomenon in which the PC-PDMS copolymer becomes clouded occurs, and thus have completed the present invention.